As explained in some detail in U.S. Pat. No. 2,701,728 issued Feb. 8, 1955 to Raymond J. Miller for a "Weight Selection Device for Stabilizing Tractors"; and U.S. Pat. No. 3,032,352 issued May 1, 1962 to Robert D. Barrett for a "Tractor Vehicle Weighting Means", it is a well known fact that the tractive effort of the tractor is limited by the weight distribution of the tractor. In Column 1, lines 44 et. seq. of the Miller patent, it is stated: "When the tractor is utilized to pull a very heavy load by a trailing draw bar, the traction forces inherently involved produce a transfer of weight from the front wheels of the tractor to the rear wheels, which weight transfer can eventually result in the front end of the tractor raising off the ground. Accordingly, when adding weight to a tractor to increase tractive effort, it is quite desirable that a substantial proportion of the added weight be located near the front extremities of the tractor; . . . "
A recently developed class of heavy duty tractors is characterized by a configuration in which the engine is supported on a chassis with a substantial portion of the engine overhanging one end of the chassis. In a farm tractor, the engine would overhang the front end of the chassis since the various earth working implements are usually coupled to the rear end of the chassis; on shovel loaders or fork lift tractors in which the shovel or lift fork are at the front of the tractor, the engine would be at the rear.
It is an object of the present invention to use the space beneath the engine overhang for conveniently mounting the counterweights. Further, the counterweight assembly is constructed and arranged so that the total mass of the counterweights may be easily and conveniently varied to provide adequate tractive effort for heavy duty operations, while permiting more efficient tractor operations on the lighter duty operations.